Rotary dust separator



Juiy 1941.-

sfe. SYLVAN ROTARY DUST SEPARATOR Filed April 7, 193a 2 Sheets-Sheet l INVENTOR. 6:5012 Sylvan BY ATTORNEY y 1941- s. e. SYLVAN 7, 28

ROTARY DUST sEPARATdR Filed April 7. 1936 4 2 Sheets-Sheet 2,

INVEIQVTOR.

Stig 6.15mi Sylvan Ma. W

A TTORNEY Patented July l, 1941 ROTARY DUST SEPARATOR Stig G:Son Sylvan, Stockholm, Sweden, assignor to American Air Filter Company, Inc., Louisville, Ky., a corporation oi Delaware Application April 7, 1936, Serial No. 73,142

8 Claims.

This invention relates to rotary dust separators of the character having an annular air passage extending from an axial inlet outwardly beyond an annular particle receiving slot to an air 'outlet and, in such passage, an impeller, which operates by rotation to centrifuge the air passing from inlet to outlet in such manneras to cause the contained particles to move toward and pass through the slot. Centrifugal devices of this character are shown in my previous Patents No, 1,941,449, dated January 2, 1934, and No. 2,039,127, dated April 28, 1936. They may be constructed and arranged to function simply as a separator or as a combined separator and blower. The present invention is particularly directed to the latter type but has some features applicable to both.

Generally stated the important objects of the invention are: to simplify the structural design and reduce the manufacturing cost of the impeller; to provide a scroll air discharge passage of good mechanical proportion without unduly sacrificing the blower characteristics; and to provide a dust receiving system of novel form and eflicient operation.

The invention is illustrated in the accompany ing drawings wherein- Figure 1 is a top plan view of a rotary dust separator embodying the features of the present invention;

Figure 2 is an end elevation sliown partly in section and corresponding to a view taken through line 2-2 of Figure 1;

Figure 3 is a front elevation;

Figure 4 is a sectional view of the housing and impeller taken through line 4-4 of Figure 3; the upper half of the impeller being shown in elevation;

Figure 5 is a section taken along line 5-5 of Figure 4;

Figure 6 is a section taken along line 6-6 of Figure 5; and

Figure 7 is a section taken along line 1-'! of Figure 4.

The invention, as illustrated, is embodied in a separator-blower type of structure having a housing I within which the impeller is mounted. The impeller, which is fixedly secured to a rotatable drive shaft 2, includes a conicallyshaped hub 3, an annular disc 4, a series of blades 5' and a band 6. The hub 3 is fixedly secured to the shaft 2 while the annular disc 4 is similarly secured to the hub 3 and arranged to extend radi ally therefrom. The annular outward pull exerted on the disc, as a result of its rotation, in-

ment.

creases from its periphery inwardly to its points of securement to the hub. Accordingly it is desirable to increase the'thickness of the disc from its periphery inwardly in order to provide the requisite strength and at the same time keep the weight of the disc at a minimum. Heretofore the disc has been cast in such form. In accordance with this invention the same result is achieved in a simple manner and at less expense by riveting or otherwise securing .together a requisite number of plates of different outside diameters. The number of plates used will depend upon the strain to be encountered and the thickness of each plate. For the most part three to five plates of suitable thickness have been found sufficient for a wide range of impeller speeds and diameters but a different number may of course be used as the occasion may require. With three plates of different diameter the strain in the outer section of the disc is carried by the largest plate, in the intermediate section thereof by the two larger plates and in the inner section by all three. The plate of largest diameter is preferably placed on the air flow side of the disc as a whole in order to provide a fiat seating surface for the blades 5.

The blades 5 are fixedly secured to the disc and arranged to project laterally therefrom across the air flow. While the blades may be shaped and arranged as desired, they are shown as of flat shape and of straight radial arrange- The blades also should be inclined to the disc in such manner as to cause particles precipitated on them during rotation to move toward that side of the air flow from which the particles are to be removed. In the structure illustrated the particles are to be removed from the disc side of the air flow and consequently the blades are inclined forwardly across the air flow from the disc l to the band 5 so that the band edges of the blades lead the disc edges thereof in the direction of rotation.

The band 6, which is secured to the adjacent side edges of the blades, operates to stiffen the blade structure as a whole. It has also been found to improve the blower characteristics of the device and for that reason is made wide enough to cover the side edges of the blades completely from their inlet to their outlet edges. In this character of device, it is desirable that the flow area at the outlet edges of the blades be not greater and preferably smaller than the' area at the inlet edges thereof. For that reason the band is made cone shaped and arranged to approach the disc as it extends outwardly so as to produce an outwardly converging centrifuging passage. the slope of the band depending upon 'the inlet-outlet area ratio desired.

The impeller is mounted in a housing I having, in its front wall I, an opening large enough to permit the insertion and removal of the impeller, and, in its rear wall 8, an opening to receive the drive shaft 2 upon which the impeller is mounted. Since the front wall opening is too large to function as an inlet opening, an axial inlet opening of suitable size is provided by a reducer member 9 which is removably secured over the front wall opening. The impeller functions to draw air through the axial inlet opening of the reducer member 9 and to centrifuge or whirl the air outwardly into a discharge passage 10 which, in accordance with usual blower practice, is

'made in the form of a volute or scroll so as to change the swirl energy from velocity to pressure. In order to minimize the diametric dimensions of the housing and secure better proportion in themechanical design thereof, the axial dimension of the scroll passage II is made larger than the corresponding dimension of the impeller. Consequently, to separate the inlet and outlet passages respectively leading to and from the impeller, the reducer member 9 is made to extend from the air inlet opening, which it forms, annularly inward to the inlet edge of the band 6 and from the front wall opening, in which it is seated, annularly inwardly to the outlet edge of the band 8, the reducer member having an intermediate portion extending along the outer side of the band with suflicient clearance to prevent rubbing. v v

In accordance with the usual blower practice the impeller may be arranged to discharge directly into the scroll passage it, in which event the inside diameter of the scroll, i. e., outside diameter of the reduced member, may be made the same as the outside diameter of the impeller except for clearance. I have discovered, however, that the change of "swirP energy from velocity to pressure can be'made more efllciently, and

the blower emciency thus enhanced, by providing,

between the outlet edges of the blades and inner side of the scroll passage it, an intermediate annular connecting'passage or outlet throat H I which increases in width as it passes radially outward. This passage is substantially unobstructed so as to permit a free outward swirling flow of air. Accordingly, the reducer member, instead of extending from the outlet edges of blades axially to the front wall of the housing, is made vto diverge outwardly from the outlet edge of. the band at an angle between the axial and radial directions for a suitable distance and then may be turned axially, if necessary, to the front'wall of the housing.

The existence and radial dimension of the outlet throat can be readily determined at the beginning or takeoff" point of the scroll discharge passage where the radial dimension of the scroll is zero except for the usual clearance. Theoretically it appears that, if perfect flow condition be assumed and flow resistance disregarded, more and more of the energy, normally lost in converting swirl energy from velocity to pressure,

can be regained simply by increasing the throat length. Practically, however, the increase in throat length is limited by the fact that it necessitates a corresponding increase in the diametric dimension of the housing. From'a practical standpoint. and unless unusual conditions permit otherwise, it does not appear advisable to noted that the air discharged through the throat H into the outlet scroll I0 is clean air, the particles originally contained in it having been discharged by the impeller into the-dust receiving system.

As mentioned previously, theimpeller blades extend from the disc 4 obliquely to the band i at an angle between the axial direction and the direction of rotation so as to cause particles precipitated on the blades to move toward the disc as they move outwardly toward the periphery of the impeller. In this manner, the particles are concentrated along the periphery of the impeller disc 4 from which they are centrifugally or radially ejected. Heretofore the particles have been ejected from the passing air through an annular slot into a circular dust ring in which they rotate with the air and from which they are caused to pass into a closed dust collecting hopper. :According to the present invention, however, the particles and that portion of the air stream, in which they are contained, both are ejected through the slot into a dustvolute or scroll and thence fed to a separator where the final separation takes place, the conveying air being returned to the impeller inlet whereby a secondary air circult is established. To'such end, a radial partition I 2, having an opening large enough to receive and clear the impeller, is cooperatively positioned over it in advance of the disc 4 to form a slot ll of desired width. The partition also is radially extended .from the impeller outwardly to the volute or peripheral wall Illa so as to form, in cooperation with it and the rear housing wall 8, .a dust scroll ll. The partition is welded or otherwise secured to the housing wall Ma and preferably braced by suitable bolts connecting it 'to the housing wall 1. Before passing it may be noted that the-impeller receiving opening. of the partition may and preferably is formed simply by blanking out of the partition stock a unitary plate of desired size. Such plate may then be cut down to desired size for use as one of the plates in the impeller disc 4.

The particle laden air passes from the dust the secondary air circuit I have found that its cleaning efiiciency depends largely upon the amount of air which it handles. For example if the secondary circuit withdraws from the pri-" mary air flow only 3% of the total air taken in by the device its cleaning efliciency will be very low, say, for one kind of particle, inthe neighborhood of 20%. An increase in secondary air ,up to approximately 7% is accompanied by a larger percentage increase in cleaning efliciency, in'fact one large enough to bring the emciency well within the useful range. If the secondary air is increased above 7% the rate of increase in the cleaning efficiency begin to decrease reaching,

zero at maximum efllciency. "with this in mind,

dust system,

. inversely proportional to its size.

and connecting it with the scroll, the axial dil and, since an increase in secondary air is also accompanied by a corresponding decrease in the amount of clean air delivered by the machine, it will be appreciated that the secondary air circuit should ordinarily be operated at a point usually around above which the percentage loss in air delivery begins to exceed the percentage gain in air cleaning efliciency and below which the reverse occurs. Operating conditions some times permit or require the sacrifice of cleaning elliciency for clean air delivery or of air delivery for cleaning efiiciency but even then the operation of the device will, for all practical purposes, be

restricted to secondary air volume limits ranging from 6 to 14%.

Where all operating conditions of a specific installation are known and no variation in secondary air contemplated, the dust system may be designed to have an air flow resistance of .such order as will restrict the volume of secondary air precisely to the desired value, say 10%. Where variations in secondary air are contemplated, the air fiow resistance of the dust system should be of such order as will permit a maximum fiow of secondary air amounting to say 14% of the air taken into the machine and the desired volume produced by increasing the resistance through the agency of a damper placed somewhere in the dust system as in the conduit I 9. Since the resistance of all of the except the dust collector, will naturally be far below the value desired in either character of design just mentioned it will be necessary either, to make the dust collector resistance high or to increase the resistance by some other means. This requirement renders the cyclone type of separator particularly suited for use in the present type of dust system because its resistance and cleaning efliciency are Consequently the desired resistance in the dust system can be obtained simply by making the cyclone small enough and in so doing not only is its cleaning efliciency increased but the amountv of space required by it is reduced to a minimum. The

- cyclone is further suited for use'with the present invention because the high dust concentrations normally obtained in the dust system is favorable to high cleaning efliciency in the cyclone.

I claim: 1. A device of the class described comprising: a housing having a volute chamber; an impeller mension of said throat increasing toward the scroll. v

3. A device of the class described comprising: a housing having an axial inlet and a volute outlet passage or scroll of substantially constant axial width; and means defining an annular gas passage extending radially outward from said inlet to said scroll, said passage having a radially converging portion in which gas may be cen-,

trifuged and a substantially unobstructed radially diverging portion connecting the centrifuging portion to the scroll.

4. An air-cleaning device of the class described comprising: a housing having an axial inlet and a volute outlet passage or scroll of substantially constant axial width; a centrifuging member rotatably mounted within said housing to receive gas axially through the housing inlet and discharge it more or less radially toward the scroll, said member having at its discharge end an axial dimension substantially less than that of the scroll; and housing means defining a substantially unobstructed annular throat passage leading radially outward from the discharge end of said centrifuging member and connecting said end with the scroll, the axial dimension of said throat passage increasing toward the scroll.

5. A device of the class described comprising: a rotatable centrifuging member having an axial inlet and a peripheral outlet; a partition, having an opening large enough to receive and clear the centrifuging member, positioned over the periphery of said member andcooperating with it to form a narrow annular slot; means cooperating with the rear side of said partition to define rower width.

rotatably mounted within said chamber to receive gas axially and discharge it more or less radially; and a partition dividing the chamber intoa clean gas scroll and a dust-laden gas scroll, said partition being interposed between the housing and the periphery of the impeller in position to separate the clean from the dustladen gas.

2. A-device of the class described, comprising: a housing having an axial inlet and a volute outlet passage or scroll of substantially constant axial width; means defining an annular centrifusin gas passage extending radially outward from said inlet toward said scroll, said centrifuging passage having at its outer end an axial dimension substantially less than that of the scroll; and means defining a substantially un-' obstructed annular throat passage leading radially outward from the centrifuging passage 6. The combination with the device of claim 5, of means cooperating with said partition to define a radially diverging annular throat passage connecting said peripheral outlet directly to the air scroll, said scroll being of volute form.

7. The combination with the device of claim 5, of means defining side-by-side tangential outlets for the air and dust scrolls, said scrolls being of volute form.

8. In combination, in a combined fan and dust collection apparatus, of a fan casing having an axial side opening for admitting dust laden air, said casing comprising asingle scroll with a partition therein comprising a skimmer plate, a single fan rotor mounted within said casing adapted to receive air and dust internally through said fan casing opening, said rotor having a back plate closely adjacent to the internal periphery of said skimmer plate located adjacent the inner ends of the fan rotor blades whereby dust impinging upon said back plate is thrown out peripherally. over the face of said plate through the opening between the periphery of the back plate and the margin of the skimmer plate closely adjacent thereto, and the dust free air isthrown out centrifugally by the rotor fan blades.

STIG GzSON SYLVAN. 

